Gums, also called hydrocolloids, are polysaccharides. Polysaccharides are polymers of simple sugar building blocks which have been in use since about 1900. Use of gums has increased throughout the century, particularly in the past 40 years, and today they are used in a wide variety of products and processes. Certain micro-organisms are capable of producing polysaccharides with properties differing from those of gums from more traditional sources. One example of such microbially-produced polysaccharides is gellan gum.
Gellan gum, first discovered in 1978 by Kelco, is produced by strains of the species Sphingomonas elodea (formerly Pseudomonas elodea), for example, strain ATCC 31461. Commercially, this gum is produced as an extracellular product by aqueous cultivation of the micro-organisms in a medium containing appropriate carbon sources, phosphate sources, organic and inorganic nitrogen sources, and suitable trace elements. The fermentation is carried out under sterile conditions with strict control of aeration, agitation, temperature and pH. When fermentation is complete, the produced viscous broth is pasteurized to kill viable cells prior to recovery of the gum. The gum can be recovered in several ways. Direct recovery from the broth yields the gum in its native or high acyl (HA) form. Recovery after deacylation by treatment with a base yields the gum in its low acyl (LA) form. Acyl groups present in the gum are found to influence its characteristics significantly.
In the native or high acyl (HA) form two acyl substituents, acetate and glycerate, are present. Both substituents are located on the same glucose residue and, on average, there is one glycerate per repeat unit and one acetate per every two repeat units. In the low acyl (LA) form, the acyl groups have been removed to produce a linear repeat unit substantially lacking such groups.
Low acyl (LA) gellan gums form gels when cooled in the presence of gel-promoting cations, preferably divalent cations, such as calcium and magnesium. The gels formed are firm and brittle. High acyl (HA) gellan gums do not require the presence of cations for gel formation, and the gels formed have structural and rheological characteristics which are significantly affected by the acyl substituents. Thus, the properties of HA gellan gels differ significantly from those of LA gellan gels. HA gellan gels are typically soft and flexible and lack thermal hysteresis.
In conventional gellan gum products, HA gellan products have been found to have a lower bulk density than LA gellan products. In fact, enzyme-treated HA gellan products have been found to have even a lower bulk density than untreated HA gellan products. The low bulk density of HA gellan products presents potential difficulties in the manufacture and use thereof (e.g., food, industrial, consumer applications). Such difficulties can limit the application scope of HA gellan products that would otherwise be available if the bulk density was greater and also complicate downstream processing (e.g., drying, milling, and the like) of HA gellan products.
It, therefore, would be desirable to provide gellan gum products that are capable of ameliorating some or all of the foregoing disadvantages. In particular, it would be desirable to provide gellan gum products with a higher bulk density.